Dopamine is involved in the control of motor function, cognition and affect (A. Dahlstrom and K. Fuxe, Acta Physiol. Scand. 232, 1-55 (1965); U. Ungerstedt, Acta Physiol. Scand. 367, 1-48 (1970)). Imbalance in the dopamine system is believed to be involved in such conditions as schizophrenia (T. Crow, Brit. J. Psychiatry 137, 383-386 (1980); Fibiger, in : The Mesolimbic dopamine system : From motivation to action, 615-37 (Eds. P. Willner and J. Scheel-Krger 1991)), Parkinson's disease (H. Ehringer and O. Hornykiewitz, Klin. Wochenschr. 38, 1236-1239 (1960), tardive dyskinesia and drug addiction (R. Wise and P. P. Rompre, Ann. Rev. Psychol. 40, 191-225 (1989); G. Koob and F. Bloom, Science 242, 715-723 (1988); G. DiChiara et al., Proc. Natl Acad. Sci. U.S.A. 85, 5272-5278 (1998)).
The dopamine transporter, a member of the large family of Na.sup.+ /Cl.sup.- dependent transporters, aids in terminating dopaminergic neurotransmission by rapid reuptake of dopamine (B. Giros and M. Caron, Trends Pharmacol. Sci. 14, 43-49 (1993). It is a major target of the psychostimulant drugs cocaine and amphetamine (B. Giros and M. Caron, Trends Pharmacol. Sci. 14, 43-49 (1993); M. Ritz et al., Science 237, 1219-1223 (1987)), but its overall role in vivo is still poorly understood.